A “firework mode” specialized for taking firework images in image sensing apparatuses such as electronic cameras has been disclosed (see, for example, Japanese Patent Laid-Open No. 2001-311977). Because the human eye has such a characteristic as to maintain an afterimage, long trails of light are perceived in a firework with the eye. In contrast, in image sensing, only trails of light corresponding to the shutter speed are imaged. For example, in still image sensing in a firework mode, therefore, image sensing control such as automatically decreasing the shutter speed is performed to express tails of light of a firework. Special exposure control such as setting the amount of exposure to a value suitable for a firework is also performed in image sensing in a firework mode, because the suitable amount of exposure cannot be obtained by the ordinary exposure control under a dark firework condition.
When a normal image sensing mode is selected in still image sensing, the shutter speed is controlled so that an amount of exposure becomes proper, and an image signal corresponding to the quantity of light to which an image sensing unit during the shutter released period is exposed is generated. In the normal image sensing mode, a shutter speed of, for example, about 1/30 second is a limit of low shutter speed for prevention of blurriness due to camera shake or blurriness due to movement of an object. When a firework image sensing mode is selected, the diaphragm is controlled so that the shutter speed is set to a predetermined value for the firework mode, and an image signal corresponding to the quantity of light to which the image sensing unit is exposed during the shutter released period is generated. While long trails of light are perceived in a firework with the human eye since the human eye has such a characteristic as to maintain an afterimage, only trails of light corresponding to the shutter speed of an electronic camera or the like are imaged in actual image sensing with the electronic camera, as described above. Therefore, it is effective to continue exposure for about 2 seconds in image sensing on a firework to express trails of light in the firework. In ordinary cases, therefore, the shutter speed determined in advance for a firework mode is about 2 seconds. FIG. 14 shows an image of an aerial firework taken at a shutter speed of 1/30 second. A firework which will be seen in a tailed state with the human eye is imaged as dots, as shown in FIG. 14. FIG. 15 shows an image of the same aerial firework taken at a shutter speed of 2 seconds. A firework can be expressed in a tailed state as shown in the figure, if the exposure period is 2 seconds.
As another processing when a firework image sensing mode is selected, control such as fixing white balance at a color temperature close to that of sunlight is performed. In firework image sensing, automatic white balancing is difficult to perform, and white balance close to that used for an image taken under sunlight is used in order to express the color of a firework approximately to the color recognized with the human eye.
The conventional image sensing apparatus has drawbacks described below. Noise is noticeable in a dark portion expressing the dark sky imaged as a background. Also, under the influence of smoke of fireworks, a dark portion is often expressed unsuitably blight. Further, while a tailed state can be expressed in a still image by decreasing the shutter speed, a tailed state cannot be expressed in moving image sensing by adjusting the exposure period, because the exposure period is limited to the moving image update period. There is also a problem that in a case where the audio frequency characteristics are optimized for audio recording in the normal image sensing mode, powerful bass sound of a firework cannot be reproduced.